In recent years, in a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS), a pixel size has been reduced. Therefore, sensitivity is lowered due to reduction in the number of photons incident on a unit pixel, and an S/N ratio is lowered. In addition, in a presently widely-used pixel array in which pixels of red, green, and blue are arranged on a plane, for example, in a Bayer array using a primary color filter, for example, in a red pixel, green and blue light does not pass through the color filter and is not used for photoelectric conversion, and therefore sensitivity is lost. In addition, when an interpolation process is performed between pixels, a false color may be generated due to generation of a color signal.
An image sensor to obtain three color photoelectric conversion signals with one pixel by stacking three photoelectric conversion layers in a vertical direction has been proposed. In Patent Document 1, as such a structure for stacking three color photoelectric conversion layers with one pixel, for example, a sensor in which a photoelectric conversion unit for detecting green light and generating a signal charge corresponding thereto is provided above a silicon substrate and blue light and red light are detected by two photodiodes stacked in the silicon substrate has been proposed.
In addition, Patent Document 2 has proposed a back surface irradiation type structure provided with a photoelectric conversion film 1 layer above a silicon substrate, having a two color photoelectric conversion unit in the silicon substrate, and having a circuit-forming surface formed on a side opposite to a light-receiving surface. When a back surface irradiation type organic photoelectric conversion layer is formed, a circuit, wiring, or the like is not formed between an inorganic photoelectric conversion unit and an organic photoelectric conversion unit. Therefore, a distance between the inorganic photoelectric conversion unit and the organic photoelectric conversion unit in the same pixel can be close to each other. Therefore, dependence of colors on an F value can be suppressed, and fluctuation in sensitivity between the colors can be suppressed.